Impacts of land use/cover change and climate variability on groundwater recharge for upper Gibe watershed, Ethiopia

Understanding the response of groundwater recharge to land use/cover change and climate variability is important for water resource management and utilization. Thus, estimating spatially and temporally distributed groundwater recharge in response to land use/cover change and climate variability are important for groundwater resource management planning. In-situ groundwater recharge measurement is challenging and limited throughout the world. Hydrologic model-based groundwater estimation is an alternative and effective method compared to the in-situ measurement in data scarce basins. However, study related to the impacts of groundwater recharge in response to environmental changes is limited in many parts of the world including in Ethiopia. This study aimed to quantify the impact of land use/cover change and climate variability on annual groundwater recharge for the upper Gibe watershed using WetSpass model for the 1985-2018 periods. Time-series satellite imageries of 1985, and 2000 and 2018 were used for land use/cover mapping. Supervised classification techniques using maximum likelihood classification algorithm were used for the land use/cover mapping. In addition, post-classification algorithm was used for land use/cover change detection. Moreover, ASTER DEM with 30 m spatial resolution and climate dataset from 1985 to 2018 were used as an input for the WetSpass model. The climate data were divided into three phases namely 1985-1996,1997-2007 and 2008-2018 for the impact assessment. The study results showed an increasing agricultural land and built-up area while declining forest, shrub, grassland and bare land during the last 30 years. Moreover, increasing temperature and declining rainfall were observed in the upper Gibe watershed during the same period. In response to these environmental changes, the annual groundwater recharge decreased from 350 mm during the first phase (i.e., 1985-1996) to 287 mm during second phase (i.e., 1997-2007) while it further declined to 221 mm during the third phase (i.e., 2008-2018) for the upper Gibe watershed. Furthermore, mean annual groundwater recharge declined by 7% from 1985 to 2018 for the upper Gibe watershed. The study indicated that WetSpass model performed well for simulating water balance and characterizing the effects of land use/cover changes and climate variability on the groundwater recharge for the upper Gibe watershed and other similar basin. This study provided baseline information for water resource experts and policymakers for further investigating the impacts of environmental changes on ground water resources and design sustainable environmental resource management and planning.